Question

如果我输入的值不同，它会起作用。它给我留下了消息文本的价值＆＃34;那本电子书不存在＆＃34;

如果我输入数据库中的确切值，它只执行但不返回任何值。为什么呢？

CREATE PROCEDURE SPBus ( 
        IN BUS VARCHAR (20)
    )  
    BEGIN

    START TRANSACTION;
    IF  NOT EXISTS (SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS,'%' )) THEN
       SIGNAL SQLSTATE '45000'
       SET MESSAGE_TEXT= 'That ebook doesnt exists';
    ELSE 
        SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS, '%');
    END IF;
    COMMIT;
END;

Answer 1

因为那时程序的其他情况将在你没有设置MESSAGE_TEXT的地方执行。试试这个：

CREATE PROCEDURE SPBus ( 
        IN BUS VARCHAR (20)
    )  
    BEGIN

    START TRANSACTION;
    IF  NOT EXISTS (SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS,'%' )) THEN
       SIGNAL SQLSTATE '45000'
       SET MESSAGE_TEXT= 'That ebook doesnt exists';
    ELSE 
        SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS, '%');
        SET MESSAGE_TEXT = 'That ebook exists';
    END IF;
    COMMIT;
END;

MySQL存储过程没有返回值

1 个答案: